RU2461950C1 - Low-frequency converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: low-frequency converter includes single-phase bridge voltage inverter, active inductance load and control system consisting of source of anti-phase clock pulses with frequency f, control element, control channels of power switches with shapers of control pulses, which are connected to control chains of the corresponding power switches of single-phase bridge voltage inverter and control element. Due to introduction to control system of generator of saw-tooth voltages with frequency 2f, two-way comparator unit, pulse distributor, limiter of maximum output voltage of control element, and in bridge inverter there are only two return diodes, and the effect is achieved with the help of their original connection diagram.

EFFECT: improving reliability.

2 cl, 4 dwg

Description

The invention relates to electrical engineering, in particular to the field of converting technology, and is intended for use in installations for electric heating of oil wells.

Known single-phase bridge autonomous voltage inverter (hereinafter AIN), made on the basis of two-operational lockable thyristors with pulse-width regulation and a DC link, made on a rectifier with a capacitor filter (Rudenko BC, Senko VI, Chizhenko IM “Fundamentals transformative technology. ”/ M.: Higher School, 1980, p.237-240). The conversion of direct voltage to alternating current for supplying an active-inductive load of a given frequency occurs by switching diagonally arranged pairs of thyristors with pulses offset by 180 ° el. When switching the keys, the electromagnetic energy of the load is discharged into the capacitor bank of the DC voltage source. The capacity of the capacitor bank C reaches a large value, especially at low frequencies f and high currents AIN:

,

,

where: I - load current;

t = 1 / f is the current flow time through the capacitor bank;

ΔU is the permissible value of the overvoltage on the capacitors.

At a current of several hundred amperes and low frequencies f (less than 5 Hz), the capacitance of a capacitor bank can reach farads, which is the main disadvantage of this device.

The closest in technical essence to the claimed solution and taken as a prototype is a low-frequency converter based on a self-contained voltage inverter (AIN) (RU 98650 U1 published October 20, 2010, Bull. No. 29), made on transistor switches, with active-inductive load and two-channel control system (see figure 1).

The power part is represented by a single-phase bridge inverter 1 with a rectifier 2, transistor switches 3 ... 6, four reverse diodes 7, 8 and an active inductive load 9. The inverter keys are controlled from a two-channel control system 10 with identical control channels 12, 13. In each channel the control contains the pulse shapers 14, 15.

The regulation of the output voltage of the inverter occurs by changing the duration τ _{2 of the} on state of the keys 4 and 6, which is determined by the elements 15 in the control channels 12 and 13 in the function of the control signal U _{p of the} control body 16. In this case, the elements 14 are drivers, and the elements 15, in addition to drivers, they contain phase shifting devices, duration shapers, and comparators. The presence of two phase-shifting devices in the system 10 leads to asymmetry of the control pulses supplied to the keys 4 and 6, which negatively affects the quality of the output voltage of the inverter 1, increases the power loss in the load 9, complicates the control system, reduces the reliability and efficiency in general. These circumstances confirm the complexity of the prototype device and its low reliability.

The technical result of the claimed device is to simplify and increase the reliability of the device.

The technical result is achieved by the fact that in a low-frequency converter containing a single-phase bridge voltage inverter, made on the rectifier, power switches, for example transistor and reverse diodes, an active inductive load and a control system consisting of a source of antiphase clock pulses with a frequency f, a control body, power key control channels with control pulse shapers connected to control circuits of the corresponding power keys of a single-phase bridge inverter a control source, and the source of antiphase clock pulses with frequency f outputs is connected to the first pulse shapers in each control channel, a sawtooth voltage generator with a frequency of 2f, a two-input comparator, a pulse distributor, a limiter of the maximum output voltage of the control body are introduced into the control system the source of the out-of-phase clock pulses is connected to the inputs of a sawtooth voltage generator, a pulse distributor, the output of the pi generator of typical voltages is connected to the first input of the two-input comparator, the second input of which is connected to the output of the control body, while the pulse distributor contains, for example, two switches whose outputs are connected to the inputs of the second pulse shapers in each control channel, and the maximum output limiter is connected to the control body voltage. A single-phase bridge voltage inverter contains two reverse diodes.

The essence of the claimed invention is that between the source of the out-of-phase clock pulses of frequency f and two identical power switch control channels, a common sawtooth voltage generator with a frequency of 2f, a comparator and a pulse distributor are included, while the outputs of the pulse distributor are connected to the inputs of the second pulse shapers of both power control channels keys, and to the governing body is connected to the limiter of the maximum output voltage. The power part of the inverter contains only two reverse diodes.

In Fig.1 shows a diagram of the prototype, Fig.2 is a diagram of the inventive device, Fig.3 shows a source of antiphase clock pulses with a frequency f of the operation diagram of the inventive device; figure 4 - chart of the inventive device.

In the diagrams of figure 1, figure 2, figure 3 adopted the following notation:

1 - single-phase bridge inverter;

2 - rectifier;

3 ... 6 - power switches, for example transistors;

7, 8 - power reverse diodes (in figure 1 there are four diodes, in figure 2 - two);

9 - active-inductive load (u, i - voltage and current in the load);

10 - control system;

11 is a source of antiphase clock pulses with a frequency f and two outputs "a" and "x" (source 11 can be performed, for example, based on a generator 26 and two comparators 27 and 28);

12, 13 - power key control channels;

14 - the first pulse shapers in blocks 12, 13 and indicated by the text FI1;

15 - second pulse shapers in blocks 12, 13 and indicated by the text FI2;

16 - governing body;

17 - a sawtooth voltage generator with a frequency of the output signal 2f, made, for example, on the elements 21 ... 23;

18 - two-input comparator;

19 - pulse distributor, consisting, for example, of two keys 24 and 25;

20 - limiter of the maximum output voltage U _{ym of the} control body 16;

21 - amplifier;

22 - key "reset" (for zeroing the capacitor in the integrator 23);

23 is an integrator.

The signals in figure 1-figure 3:

U _and - the voltage of the pulses "reset" at the output 21;

U _p - sawtooth voltage at the output 23;

U _у - control voltage at the output 16;

U _p - input voltage 16.

Notes:

1. In the inventive device, the pulse shapers 14 and 15 consist of drivers and do not contain other devices. Compared with the prototype, in which the pulse shapers 15 are more complex nodes and contain, in addition to drivers, phase-shifting devices, comparators and pulse shapers.

Designations of figure 4:

The signals U ₁ , U ₂ , a, x, U _and , U _p , U _y are given in the notation of figure 2;

FI1 - 12 (14), FI2 - 12 (15) - the corresponding pulse shapers 1 and 2 in the control channel 12, their digital designations 14 and 15;

FI1 - 13 (14), FI2 - 13 (15) - the same, but in the control channel 13;

τ ₁ , τ ₂ - pulse durations respectively at the outputs of blocks 14, 15 in the control channels 12 and 13;

τ ₁ (3), τ ₁ (5) - the duration of the control pulses on the power switches 3 and 5;

τ ₂ (4), τ ₂ (6) - the same on power switches 4 and 6;

t ₁ - rise and fall times to zero load current i;

Δt - pulse time "reset" U _and ;

U _d is the voltage at the output of rectifier 2;

u, i - respectively, the voltage and current in the load 9.

The device contains a single-phase bridge inverter 1, consisting of a rectifier 2, power switches 3 ... 6, for example, transistor and two reverse diodes 7, 8, an active inductive load 9 and a control system 10, consisting of a source of antiphase clock pulses 11 with a frequency f of two identical control channels 12, 13 with power keys with two pulse shapers 14, 15 in each, respectively connected to the control circuits of power keys 3 ... 6, of the control body 16. In addition, there are two-input sawtooth voltage generator 17 s 2f frequency and a comparator 18, the first input of which is connected to the sawtooth voltage generator 17, and the second input is connected to the control body 16. The input of the pulse distributor 19 is connected to the output of the comparator 18, and both of its outputs are connected to the second pulse shapers 15 of the power switch control channels 12 and 13. An output voltage limiter 20 is connected to the governing body 16. The inputs of the first pulse shapers 14 of the control channels 12, 13 are connected to the outputs of the antiphase clock pulses source 11; the inputs of the sawtooth voltage generator 17, containing the amplifier 21, the "reset" key 22 and the integrator 23, as well as the inputs of the keys 24, 25 of the pulse distributor 19.

The operation of the claimed device is as follows.

At the outputs "a" and "x" of the clock source 11, two antiphase sequences of pulses are formed with a given frequency f, which, with the help of a sawtooth voltage generator 17, is converted into a sawtooth voltage U _p with a frequency of 2f. This is done, for example, using an amplifier 21, a “reset” key 22, and an integrator 23. This process is reflected in the four upper diagrams in FIG. 4, where U ₁ and U ₂ are the voltage at the outputs “a” and “x” of block 11. impulse voltage U _and is formed at the outlet 21 and enters the key 22, a short time (during Δt) shunt capacitor integrator 23, performing "reset""saw" from maximum to zero twice per period T = 1 / f. The signal U _p is fed to the first input of the comparator 18, and the signal U _y from output 16 is received at its second input. As a result of comparing these signals, output signal U ₃ (Fig. 4, e) with a frequency of 2f, which, passing through the keys 24, 25 at the inputs of the pulse shapers FI2 (15) in blocks 12, 13, turns into two antiphase signals U ₄ and U ₅ with a duration of τ ₂ and a frequency f (Fig. 4, e and Fig. 4, g). In this case, in FIG. 1 (14) in blocks 12, 13, signals U ₁ and U ₂ are received with a frequency f (Fig. 4, a and Fig., 4b). As a result, at the outputs of each of the control channels 12 and 13, two sequences of pulses of different durations τ ₁ and τ ₂ occur (Fig. 4, s - 4, l). In this case

τ ₁ = T / 2-Δt≈1 / 2f> τ ₂ ,

where T = 1 / f is the period of the frequency f, Δt << τ ₁ is the pulse duration U _and , necessary to exclude the emergency mode of simultaneous operation of the series-connected power switches (3, 4 and 5, 6), as well as for the discharge of the capacitor in the block 23 through key 22 and a microsecond component. The duration τ _{2 is} determined by the signal U _y (points N ₁ and N ₂ in FIG. 4, d) and determines the output voltage at load 9 (FIG. 4, m).

In each channel, the leading edges of the control pulses from outputs 14 and 15 coincide, and the trailing edges differ by the value τ ₀ -Δt≈τ ₀ , which should be greater than the time t _{1 of} the current falling off in the load to zero. The current i drops through the included power switch, for example 3, and diode 8 (or switch 5 and diode 7) in Fig. 4, m. The value of t ₁ is determined by the electromagnetic time constant of the load circuit T _e and is equal to

t ₁ ≈4T _e = 4L / R.

The limiter of the maximum output voltage 20 provides a limitation of the maximum value of τ ₀ , which eliminates the emergency mode of a short circuit in the inverter, for which it is necessary: τ ₀ (U _{at max} )> t ₁ .

The operation of power keys is explained in figure 4, n.

The effective value of the voltage at the load 9 is determined by the formula:

where τ ₂ is the adjustable duration in seconds, f is the frequency in hertz.

The value of τ ₂ depends on the value of the control voltage U _y

where U _p.m - the maximum voltage of the "saw".

Formula (2) is valid provided

what takes place in this case, where a = 1 ÷ 10 Hz.

Combining formulas (1) and (2), we finally have:

- относительная величина напряжения управления.Where

is the relative magnitude of the control voltage.

, что очевидно из фиг.4, м.So, with

, which is obvious from figure 4, m

It should be noted that the source of clock pulses 11 can be performed according to various schemes, one of which is shown in Fig.3, and is based on a sinusoidal oscillator 26 and two comparators 27, 28.

Due to a certain threshold of operation of the comparators at the outputs "a", "x" we have pulses in accordance with figure 4.

Thus, in the inventive device due to the introduced into the control system of the sawtooth voltage generator with a frequency of 2f, two-input comparator, pulse distributor, limiter of the maximum output voltage of the control body, as well as simplification of the second pulse shapers in each channel, as well as the original circuit of their connection, technical result.

Claims (2)

1. A low-frequency converter containing a single-phase bridge voltage inverter made on a rectifier, power switches, for example transistor and reverse diodes, an active inductive load and a control system consisting of a source of antiphase clock pulses with a frequency f, a control body, control channels for power keys with drivers of control pulses connected to the control circuits of the corresponding power switches of a single-phase bridge voltage inverter and control body, an IR of out-of-phase clock pulses with a frequency of f outputs is connected to the first pulse shapers in each control channel, characterized in that a sawtooth voltage generator with a frequency of 2f, a two-input comparator, a pulse distributor, a limiter of the maximum output voltage of the control body are introduced into the control system, while the source is out of phase clock pulses outputs connected to the inputs of the sawtooth voltage generator of the pulse distributor, the output of the sawtooth voltage generator connected to the first input of the two-input comparator, the second input of which is connected to the output of the control body, while the pulse distributor contains, for example, two keys, the outputs of which are connected to the inputs of the second pulse shapers in each control channel, and the limiter of the maximum output voltage is connected to the control body. 2. The low-frequency Converter according to claim 1, characterized in that the single-phase bridge voltage inverter contains two reverse diodes.

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